1. Field of the Invention
The present invention relates to a method of improving an image quality, and, more particularly, to a method of improving an image quality by differentiating text from pictures and using the differentiated result when a document, on which text and pictures are mixed, is scanned and input from an image input apparatus.
2. Description of the Related Art
U.S. Pat. No. 4,996,603 discloses an image processing system. An input subject pixel is determined to be a text pixel or a picture pixel, and the text pixel is processed as a fixed slice, and the picture pixel is processed as a halftone. Here, the halftone process is used to print black-and-white photographs on newspapers or on magazines, and outputs in two values, that is, in two levels of black and white to display a gray scale. The halftone processing is suitable for processing images in a case in which actual gray output of a high image quality cannot be made, but the two-level output is required. However, the halftone processing lowers the resolution since the image is blocked into predetermined decomposition areas.
The above cited reference discloses three detection circuits to find the text. The detection circuits are a successive gray color detection circuit, a fine line detection circuit, and a black color detection circuit. The successive gray color detection circuit inspects repetition in a predetermined period by setting the highest brightness limit, the fine line detection circuit calculates a difference between adjacent pixels, and the black color detection circuit inspects the repetition of brightness under the lowest brightness limit.
However, in a case in which a screened halftone pattern is shown on the image, the high brightness pixel is represented intermittently, thus incorrectly causing the picture to be recognized as text. Here, the screened halftone refers to a distortion shown in data formed by scanning a halftone image output after a picture area is halftone processed. When the screened halftone pattern is shown on the image, the pixel having a higher brightness, that is, having a brightness higher than a predetermined limit, is shown intermittently, and the probability of incorrect recognition of the picture as text increases. Therefore, when a halftone processed document is scanned, the halftone processed picture may be recognized as text. When the incorrectly recognized text is processed, a highly distorted output can be shown when the image is reproduced.
U.S. Pat. No. 6,227,725 discloses a method for improving text process for a color and gray scale document. This method calculates the brightness, chromaticity, and gradient of the subject pixel, differentiates the subject pixel roughly as a text pixel, picture pixel, or a background pixel, and suppresses the background pixel while widening the area determined to contain the text pixel using connect components.
However, according to the above cited reference, since the pixels located on an edge of the text and an adjacent area only are determined to be text, an inner part of the text of medium or larger size is determined to be a picture. Also, the image is processed in a pixel unit, and after that, the area determined to contain the text is expanded using the connect components. However, the texts and pictures cannot be differentiated by a desired area unit. That is, since the picture and text pixels are mixed on the image, the image quality of the output document is lowered unless the differentiation is made in an area unit.